Method for forming a foundation in the ground

ABSTRACT

A method of forming a foundation in the ground, comprising the steps of—forming a foot (11) in the ground (100); —forming a column (12) made from a load bearing material in the ground (100) on top of the foot (11); and —forming a pile (13) in the material column (12) such that the pile (13) extends down to the material foot (11) or into the material foot (11).

TECHNICAL FIELD

This disclosure in general relates to a method for forming a foundationcapable of bearing a load in the ground.

BACKGROUND

Rigid bodies, such as concrete piles may be used as foundations in theground for any kind of structure when a load bearing capability of theground is not high enough to support the structure on a shallowfoundation. There is a need for a cost saving method for producing afoundation in the ground.

SUMMARY

One example relates to a method. The method includes forming a materialfoot in the ground, forming a material column on top of the materialfoot, and forming a pile inside the material column such that the pileextends down to the foot or into the foot.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples are explained below with reference to the drawings. Thedrawings serve to illustrate certain principles, so that only aspectsnecessary for understanding these principles are illustrated. Thedrawings are not to scale. In the drawings the same reference charactersdenote same features.

FIGS. 1A to 1C illustrate one example of a method for forming afoundation in the ground, wherein the foundation includes a pile and abedding of the pile, wherein the bedding includes a material foot and amaterial column;

FIG. 2 illustrates one example of a depth vibrator in greater detail;

FIGS. 3A to 3C illustrate method steps for producing the material footaccording to one example;

FIGS. 4A and 4B illustrate one example of a method for forming the pileof the foundation in the bedding;

FIGS. 5A and 5B illustrate another example of a method for forming thepile;

FIGS. 6A and 6B illustrate yet another example of a method for formingthe pile;

FIG. 7 illustrates one example of a concrete pile manufactured in aconventional way using a so-called continuous flight auger method; and

FIG. 8 illustrates another example of a foundation, wherein thisfoundation has been formed without a material column.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings. The drawings form a part of the description andfor the purpose of illustration show examples of how the invention maybe used and implemented. It is to be understood that the features of thevarious embodiments described herein may be combined with each other,unless specifically noted otherwise.

One way of forming a foundation capable of bearing a load includesramming a precast rigid element, such as a concrete pile into theground. As a load transfer from a pile into surrounding soil happens inpart by friction along sidewalls of the pile but to a large part also bythe load bearing on the bottom of the pile, a foundation based on pilesoften requires that the piles are long enough to reach a stable groundregion, such as a stiff or dense soil layer or a rock region, capable ofbearing large parts of the load provided by the structure through thebottom of the pile. When the pile hits an obstacle in the ground, suchas a rock embedded in sand or clay, the prefabricated pile often has tobe cut off along the ground surface and is “lost” for future loadbearing.

Another way of forming a pile in the ground includes drilling a hole andfilling the hole with concrete. This method, similar to driving aprecast concrete pile into the ground, requires that the hole is drilleddown to a stable ground region capable of bearing the load provided by astructure.

Concrete piles with an enlarged foot, for example so called Frankipiles, may be used to form foundations even in a loose ground, such asloose sand or silt, when solid ground regions are too deep to be reachedcost efficiently by ramming precast piles into the ground or by drillingholes. These Franki piles are formed by ramming a tube filled at thebottom with gravel or dry concrete into the ground and by driving, witha falling weight, the concrete or gravel from the tube into the groundafter the tube has reached a desired depth. By driving the concrete orgravel in the ground a foot having a diameter larger than the diameterof the tube is formed. After installation of such foot, and whilewithdrawing the tube from the ground, the pile is completed by fillingthe hole formed by the tube with concrete down to the foot. This method,however, is slow and, therefore, expensive.

There is therefore a need for a method for forming foundation capable ofbearing a load in the ground, wherein the method is inexpensive andsuitable to produce the foundation in loose ground. One example of suchmethod is illustrated in FIGS. 1A to 1C.

Referring to FIG. 1A, the method includes forming a foot 11 in theground 100. More specifically, forming the foot 11 includes forming thefoot 11 spaced apart from a ground surface 101. The foot 11 may beformed in various ways.

According to one example, illustrated in FIG. 1A, forming the foot 11includes introducing material into the ground and forming the foot 11using a vibrator arrangement 2. In this case, the foot 11, which mayalso be referred to as material foot, is formed such that a diameter d1of the material foot 11 is larger than a diameter d2 of the vibratorarrangement 2. One example of a method for forming the material foot 11using the vibrator arrangement 2 is explained in greater detail hereinfurther below.

Various materials or combinations of various materials may be used toform the material foot 11. According to one example, the material foot11 is formed from concrete. According to another example, the materialfoot 11 is formed from a granular material, such gravel or sand.Optionally, the material foot 11 includes a granular material and grout.In the case of forming the material foot using a vibrator arrangement,grout may be injected from grouting nozzles (not shown) attached to thevibrator arrangement 2 at the same time as the granular material isintroduced into the ground, wherein the grout provides for a bondingbetween the stones or grains of the granular material of the materialfoot 11.

Referring to FIG. 1B, the method further includes forming a materialcolumn 12 on top of the material foot 11. Referring to FIG. 1B, thematerial column 12 may extend from the material foot 11 to the groundsurface 101. The material column may be formed from one or moredifferent materials. These materials include, for example, gravel orsand. The gravel may include angular gravel or rounded river gravel.According to one example, the material column is formed from only onematerial, such as gravel or sand.

According to another example, the material column is formed from two ormore different materials, such as gravel and sand. When forming thematerial column from two or more materials the column may be formed suchthat it includes two or more column sections, wherein each columnsection only includes one material, such as gravel or sand. The type ofmaterial and, optionally, the size of the material particles may beselected dependent on the type of soil in which the respective columnsection is formed. The ground may include different soil layers oneabove the other, wherein for each column section formed in a respectivesoil layer the column material can be selected independently. Accordingto another example, the material column or at least one section of thematerial column is formed from a mixture of two or more differentmaterial, such as sand and gravel.

Referring to FIG. 1C, the method further includes forming a rigid pile13 inside the gravel column 12 such that the rigid pile 13 extends downto the material foot 11 or, as illustrated in FIG. 1C, is partiallyembedded into the material foot 11.

A foundation of the type illustrated in FIG. 1C that includes a foot 11,a material column 12 on top of the material foot 11, and a rigid pile 13inside the material column 12 provides an increased lateral support ofadjustable magnitude over depth, as compared to a conventionalfoundation formed in the ground. This higher lateral support can bebeneficial to increase the portion of the load to the pile 13 that iscarried by a shaft of the pile 13 as compared to a bottom of the pile13, wherein the bottom of the pile 13 is the section of the pile 13 thatfaces the foot 11. Higher lateral support can also be beneficial toreduce the moment load in the pile shaft when the pile is horizontallyloaded or loaded by a moment on the pile head, wherein the pile head isa section of the pile facing away from the foot 11.

The vibrator arrangement 2 that may be used for forming the materialfoot 11 is only schematically illustrated in FIG. 1A. Vibratorarrangements for introducing material into the ground are known.Nevertheless, for a better understanding, one example of a vibratorarrangement 2 is briefly explained with reference to FIG. 2 in thefollowing. Referring to FIG. 2, the vibrator arrangement 2 includes asilo tube 21, a vibrator 23, which may also be referred to as vibroflot,coupled to the silo tube 21 and including a tip 25. The tip 25 forms alower end of the vibrator arrangement 2. The vibrator 23 may be coupledto the silo tube 21 by a damper element 22. Further, the vibratorarrangement 2 includes a pipe 24 connected to the silo tube 21 andextending from the silo tube 21 towards the lower end of the vibratorarrangement 2, wherein the pipe 24 has an outlet 26 at the lower end ofthe vibrator arrangement 2. At an upper end, which is not shown in FIG.2, the vibrator arrangement 2 includes an inlet 27 (illustrated in FIG.1A), wherein material can be fed into the silo tube 21 via the inlet 27.Material fed into the silo tube 21 can be introduced into the ground 100via the outlet 26 of the pipe 24 connected to the silo tube 21. The silotube 21 may include one or more locks in order to apply excess airpressure in the silo tube 21 to control material flow from the input 27to the outlet 26 against the in-situ pressure in the soil. Such locks,however, are not illustrated in the drawings.

In operation, the tip 25 of the vibrator oscillates (repeatedly moves)in lateral directions, which are directions parallel to the groundsurface 101 and perpendicular to a longitudinal direction of pipe. Inthis way, the vibrator 23 laterally compacts the ground and createsspace for the vibrator arrangement 2 to move into the ground, justdriven by its own weight.

The vibrator arrangement 2 illustrated in FIG. 2 includes one pipe 24and one outlet 26. This, however, is only an example. According toanother example (not illustrated) two or more pipes extend from the silotube 21 along the vibrator 23 to the lower end of the vibratorarrangement 2.

FIGS. 3A to 3C illustrate, in greater detail, one example of a methodfor forming the foot 11 in the ground 100 using a vibrator arrangement.Referring to FIG. 3A, this method includes introducing the vibratorarrangement 2 to a predefined depth into the ground 100. The vibratorarrangement 2 may be held by a suitable device, such as an excavatorarm, and may be lowered or lifted by this device. For introducing thevibrator arrangement 2 into the ground 100, however, no external forceis required. The vibrator arrangement 2 penetrates into the ground 100just supported by its own weight and vibrations of the vibrator 23,wherein these vibrations of vibrator 23 create a space at the lower endof the vibrator arrangement 2 that enables the vibrator arrangement 2 topenetrate deeper into the ground 100. When the vibrator arrangement hasreached the predefined depths, the device holding the vibratorarrangement 2 may stop lowering the vibrator arrangement 2 so that thevibrator arrangement 2 stops penetrating deeper into the ground 100.Referring to FIG. 3B, the method further includes lifting the vibratorarrangement 2 and introducing material 11′ into a space below the lowerend of the vibrator arrangement 2, wherein this space has been createdby the vibrator arrangement 2. According to one example, the silo tube21 has been filled with material before, so that automatically when thevibrator arrangement 2 is lifted the material 11′ is introduced into theground via the silo tube 21 and the pipe 26.

Referring to FIG. 3C, the method further includes lowering the vibratorarrangement 2 into the material 11′. In this way, the material 11′ iscompacted and driven mainly radially into the ground surrounding thespace into which the material 11′ had been introduced.

Forming the material foot 11 may include repeating the method stepsillustrated in FIGS. 3A to 3C several times, that is, (a) lifting thevibrator arrangement 2 in order to introduce material 11′ into theground 11, and (b) penetrating into the introduced material 11′ by thevibrator arrangement 2 in order to compact the material 11′ and drivethe material into ground regions surrounding the material. A size of thematerial foot 11, that is, a height of the material foot 11 in adirection perpendicular to the ground surface 101, and a width ordiameter d1 of the material foot 11 in directions parallel to the groundsurface 101 are dependent on an amount of material that is introducedinto the ground 100. The amount of material increases as the number ofrepetitions of the method steps illustrated in FIGS. 3A to 3C increases.

According to one example, the material 11′ introduced into the ground100 and forming the material foot 11 may be concrete. This concrete isintroduced into the ground in liquid form, wherein the concrete cures(hardens) after being introduced into the ground 100.

According to another example, the material 11′ introduced into theground 100 in order to form the material foot 11 is gravel, wherein thegravel is compacted by a method step of the type illustrated in FIG. 3C.Optionally, liquid grout may be introduced into the gravel by thevibrator arrangement 2 either from time to time in the process offorming the material foot 11 or after the gravel forming the materialfoot 11 has been introduced. The liquid grout flows between the graveland finally cures so that a solid material foot 11 is formed.

Referring to the above, the material foot 11 is formed such that thediameter d1 of the material foot 11 is greater than a diameter d2 of thevibrator arrangement 2. The diameter d2 of the vibrator arrangement 2essentially equals the diameter of a hole the vibrator arrangement 2forms when penetrating into the ground 100. Due to irregularities in theground and variations in the manufacturing process of the material foot11 the material foot 11 might not have the same diameter along itsentire height. According to one example, as used herein “the diameter d1of the material foot 11” is an average diameter of the material foot 11.

According to one example, the diameter d1 of the material foot 11 is atleast two times the diameter d2 of the vibrator arrangement 2, d1≥2*d2.According to one example, the diameter d1 of the material foot 11 isbetween two times and five times the diameter d2 of the vibratorarrangement 2, 2*d2≤d1 5*d1. According to one example, the diameter d1of the material foot 11 is between 0.5 meters (m) and 2 meters.

According to an example, the diameter d1 of the material foot 11 iscontrolled by controlling or monitoring at least one operating parameterof the vibrator arrangement. According to one example, the at least oneoperating parameter is a power consumption of the vibrator 23 when thevibrator arrangement 2 (by its weight and vibrations of the vibrator 23)is driven into the material of the material foot 11. Depending on thetype of motor drive used in the vibrator arrangement 2, the powerconsumption may be measured by measuring an electric power consumptionof a motor of the vibrator arrangement 2 or by measuring a hydraulicpressure in a motor of the vibrator arrangement 2. The power consumptionof the vibrator 23 required to penetrate into the introduced material isa function of the stiffness/density of the material and also the soilthat surrounds the material into which the vibrator arrangement 2penetrates. In other words: The stiffer or denser the material, thehigher is the power consumption and the higher is also the lateralconfinement between the installed column 12 and the surrounding soil.According to one example, in order to achieve a material foot 11 with adesired stability, the power consumption is measured and the methodsteps of lifting and lowering the vibrator arrangement 2 is repeateduntil the power consumption reaches a predefined threshold. Basically,the weaker the ground, the greater the diameter of the material column12 will be before a desired power consumption threshold is reached.

Alternatively or in addition to monitoring the power consumption of thevibrator arrangement 2 an acceleration or a velocity of the vibratorarrangement 2 may be monitored. This may be achieved by placing one ormore accelerometers or velocity sensors at the vibrator arrangement 2.The measured acceleration or velocity, similar to a power measurement,can be correlated with the confinement generated by the vibratorarrangement 2 while building the foot 11.

Operating parameter control during installation of the material foot 11can lead to a better quality of such material foot 11 since the foot'slateral confinement with the in-situ soil can be controlled bycontrolling the Operating parameter. In a very loose soil, for example,the foot 11 would have to be built bigger to reach the same powerconsumption in the motor than this would be the case in a less loosesoil. Thereby building the foot 11 power controlled will give a bettercontrol over the effort spent versus the result obtained.

There may be soils, such as sandy soils, in which an operating parametercontrolled formation of the foot 11 will not achieve a satisfyingresult. Thus, according to another example, forming the material foot 11using a vibrator arrangement includes introducing a predefined amount ofmaterial into the ground 100 and compacting the material using thevibrator arrangement 2.

Referring to the above, forming the material foot 11 using a deepvibrator 23 is only one of several different examples for forming thematerial foot 11. According to another example, the material foot isformed in accordance with forming the material foot in the Franki pilemethod explained above. In this case, forming the material footincludes: ramming a tube filled at the bottom with gravel or dryconcrete into the ground; and driving, with a falling weight, theconcrete or gravel from the tube into the ground. By driving theconcrete or gravel in the ground a foot having a diameter larger thanthe diameter of the tube is formed. The foot 11 has a diameter largerthan a diameter of the tube. The diameter of the material foot 11 may bebetween two times and five times the diameter of the tube. According toone example, the diameter d1 of the material foot 11 is between 0.5meters (m) and 2 meters.

According to yet another example, forming the material foot 11 includes:ramming a tube having a lock at its lower end into the ground until thetube reaches a desired depth; partially filling the tube with gravel ordry concrete; withdrawing the tube and opening the lock so that thefilling material is introduced into a hole below the tube; closing thelock and driving the tube into the material at least once. The tube maybe lifted and driven into the material several times. The lock may beimplemented in such a way that it automatically opens when the tube islifted and closes when the tube is driven into the material. The foot 11has a diameter larger than a diameter of the tube. The diameter of thematerial foot 11 may be between two times and five times the diameter ofthe tube. According to one example, the diameter d1 of the material foot11 is between 0.5 meters (m) and 2 meters.

Again, forming the foot 11 using one of the methods explained above arejust examples. Other examples include: forming the foot using any typeof top driven mandrel with or without a lock; forming the foot 11 usinga rotary bottom feed stone column technique; forming the foot 11 using atop feed technique, wet or maybe even dry; or the like.

Referring to the above, the vibrator arrangement 2 may penetrate intothe ground 100 just supported by its own weight and vibrations of thevibrator 23. Further, referring to FIGS. 3A-3C, the ground may includedifferent soil layers 110-140, wherein one or more of these soil layersmay be too stable for the vibrator arrangement 2 to penetrate through.In this case, the hole at the bottom of which the material foot 11 isformed by the vibrator arrangement 2 is at least partially predrilled.That is, a hole is formed by a drilling device such that the holeextends through soil layers impenetrable by the vibrator arrangement 2.After removing the drilling device, the vibrator arrangement is loweredinto the predrilled hole in order to form the material foot 11 asexplained above. A depth of the predrilled hole may correspond to thedesired depth of the hole at the bottom of which the material foot is tobe produced. Alternatively, the predrilled hole is less deep as desiredand the vibrator arrangement 2 is used to extend the hole to the desireddepth. A diameter of the predrilled hole may be less than the diameterof the vibrator arrangement 2. The drilling device is an auger, forexample.

At least partially pre-drilling the hole is not restricted to a methodin which the material foot 11 is produced using a vibrator arrangement.The hole may also be pre-drilled when forming the material foot 11 inaccordance with any one of the other methods explained above.

In the examples explained above, foot 11 is a material foot that isformed by introducing material into the ground. This, however, is onlyan example. According to another example, forming the foot 11 includescompacting ground material. A foot 11 formed in this way may be referredto as in-situ foot. Forming an in-situ foot may include using a vibratorarrangement 2 of the type explained above, introducing the vibratorarrangement 2 to a predefined depth, and repeatedly lifting and loweringthe vibrator arrangement. The foot 11 may be formed in this way in asandy soil layer, for example, wherein each time the vibratorarrangement 2 is lifted ground material flows into the space below thevibrator tip 25 and is compacted when the vibrator arrangement islowered. The vibrator arrangement 2 may be implemented without a tube inthis example. In the case that a cavity is formed above the foot 11 dueto material flow, this cavity is filled by the material column 12 formedlater in the process.

In each case, the material column 12 is formed in the hole above thefoot 11, wherein this hole is formed by the vibrator arrangement 2 whenpenetrating into the ground (see FIG. 1B), or by any other kind of tubeused in the manufacturing process of the foot 11. Forming the materialcolumn 12 may include simply filling the hole with material.

Filling the hole with material may be achieved by feeding the columnmaterial via the tube 26 of the vibrator arrangement 2 or via any otherkind of tube into the hole when the vibrator arrangement 2 or the tubeis withdrawn from the hole. Alternatively, the vibrator arrangement 2 ortube is withdrawn from the hole and gravel is filled into the hole afterthe vibrator arrangement 2 has been withdrawn. The latter may be appliedwhen the ground is stable enough that the hole formed by the vibratorarrangement 2 remains open after the vibrator arrangement 2 or the tubehas been withdrawn from the ground.

According to another example, the material column 12 is formed using awet top feed method. This method uses a deep vibrator that does not havea material pipe attached to it. Instead, the material forming thematerial column 12 is fed in an annular space around the vibrator,wherein the space is kept open by flushing water from the vibrator tip.

Referring to the above, the material column may include two or morecolumn sections formed from different materials or materialcombinations. A material column of this type may be achieved byintroducing different materials or different material combinations intothe hole at different times of the filling process.

According to another example, forming the material column 12 includesforming the material column 12 using a vibrator arrangement and usingthe same kind of method steps explained with reference to FIGS. 3A to3C, that is, lifting the vibrator arrangement 2 and introducing materialinto a space below the lower end of the vibrator arrangement 2 andcausing the vibrator arrangement 2 to penetrate into the introducedmaterial in order to compact the material and laterally drive thematerial into the ground. The vibrator arrangement may be the samevibrator arrangement used to form the material foot 11 or a differentvibrator arrangement. Forming the material column may include formingseveral column segments (column sections) one above the other. Accordingto one example, a diameter of the material column 12 is lower than thediameter d1 of the material foot 11. This may be achieved by forming thematerial columnl2 such that in each segment of the gravel column 12having essentially the same height as the material foot 11 the number ofrepetitions is lower than the number of repetitions used to form thematerial foot 11. The diameter d1 of the material column 12 is largerthan the diameter d2 of the vibrator arrangement 2 (d1>d2). According toone example, the diameter of the material column is between the diameterd2 of the vibrator arrangement 2 and 1.5 times the diameter d2 of thevibrator arrangement 2 (d2<d1<1.5*d2).

According to one example, which may result in a particularly highbearing capacity of the rigid body, the number of repetitions whenforming the gravel column is controlled dependent on at least oneoperating parameter, such a power consumption, an acceleration, avelocity, etc of the vibrator 23. The power consumption may be measuredby measuring an electric power consumption of a motor of the vibratorarrangement 2 or by measuring a hydraulic pressure in a motor of thevibrator arrangement 2, depending on the type of motor drive used. Theacceleration and the velocity may be measured using suitable sensors.

The power consumption, the acceleration, or the velocity of the vibrator23 required to penetrate into the introduced material is a function ofthe stiffness/density of the material and also the soil that surroundsthe material into which the vibrator arrangement 2 penetrates. In otherwords: The stiffer or denser the material, the higher is the powerconsumption, the lower is the acceleration and the velocity, and thehigher is also the lateral confinement between the installed column 12and the surrounding soil. According to one example, in order to achievea material column 12 with a desired stability, at least one operatingparameter is measured and the method steps of lifting and lowering thevibrator arrangement 2 is repeated until the operating parameter in eachinstallation depth interval reaches a respective predefined threshold.The vibrator arrangement 2 is then lifted to a greater extent andforming a new segment of the gravel column 12 starts, wherein formingeach segment includes lowering the vibrator arrangement 2 into theintroduced material at least once. Dependent on the stiffness/density ofthe surrounding ground 100 the diameter of the material column 12 mayvary along its length. Basically, the weaker the ground, the greater thediameter of the material column 12 will be before a desired operatingparameter threshold is reached.

A load transfer between the concrete pile 13 and the soil surroundingthe material column 12 happens at least in part by shaft frictionbetween the material column 12 and soil. Based on this, it may generallybe beneficial to increase such shaft friction also in weak layers byraising the lateral stress in such layers by means of the powerconsumption-controlled installation of the gravel column 12.

Basically, by controlling at least one operating parameter the column 12can be produced in such a way that the lateral confinement stress causedby the column 12 is essentially the same at each longitudinal positionof the material column 12. This, however, is only an example. Ingeneral, monitoring at least one operating parameter makes it possibleto control the lateral confinement stress, wherein it may be desirableto vary the lateral confinement stress according to soil mechanicalrequirements of the particular pile 13 that is embedded in such column12.

In cases where the pile 13 has to carry high horizontal loads it couldfor example be beneficial to concentrate a larger effort into building astrong gravel column 12 in the uppermost part of such column 12 so thatthe horizontal bedding to transport such horizontal loads from the pile13, via the gravel column 12 into the soil is highest. In cases wherefor example an upper sand fill is placed on a soft clay and below thesoft clay is the load bearing stratum for the pile, it could bebeneficial to have a very low bedding in the sand layer to minimizeadded loading onto the pile 13 from what is well known as the so callednegative skin friction acting from the sand via the gravel column ontothe pile shaft and hence unwanted increasing its load. In suchparticular scenario the gravel column 12 could in the sand layer bereplaced by a material that has very low friction (clay slurry forexample).

In order to be able to control formation of the material column 12 theground may be analyzed beforehand. Analyzing the ground may include anykind of analytical processes that provides information on stability,thickness, etc. of individual ground layers. One method of analyzing theground 100 includes measuring a power consumption of a vibratorarrangement when it penetrates into the ground in the process of formingthe material foot 11 and/or the material column 12.

The pile 13 inside the gravel column 12 may include various kinds ofmaterials and may be formed in various ways. According to one exampleillustrated in FIGS. 4A and 4B, the method includes forming the pile 13as a concrete pile using a vibrator arrangement 30. This vibratorarrangement 30 may have a lower diameter than the vibrator arrangement 2used to form the material foot 11. This however, is only an example. Thediameter of the vibrator arrangement may also be larger than thediameter of the material column 12. Referring to FIG. 4A, forming theconcrete pile 13 includes forming a hole in the gravel column 12 by thevibrator arrangement 30 such that the hole in the gravel column 12extends down to the material foot 11 or into the material foot 11.According to one example, the hole extends into the material foot 11such that a depth of the hole in the material foot 11 is between 0.3times and 0.5 times the height of the material foot 11.

Referring to FIG. 4B, forming the pile 13 includes withdrawing thevibrator arrangement 30 from the ground 100 and introducing liquidconcrete into the hole formed by the vibrator arrangement 30. Formingthe pile 13 in this way may be referred to as cast in place piling. Theconcrete may be introduced into the hole via the vibrator arrangementwhile withdrawing the vibrator arrangement 30 from the hole. In additionto concrete the pile 13 may include a reinforcement cage. The hole isfilled with concrete, either via the vibrator arrangement 30 or afterwithdrawing the vibrator arrangement 30 from the hole, and thereinforcement cage is inserted after filling the hole with concrete.Inserting the reinforcement cage may include using a vibrator or anyother kind of device capable of driving the reinforcement cage into theliquid concrete.

Forming the pile 13 by cast in place piling may result in a highfriction between the concrete pile 13 after curing and the materialcolumn 12, wherein the friction is particularly high when the materialcolumn is at least partially formed from angular gravel.

According to another example, forming the pile 13 includes forming theconcrete pile 13 from gravel and grout, wherein both grout and gravelare introduced into the hole via the vibrator arrangement 30. Gravel andgrout may be introduced into the hole at the same time. Alternatively,gravel and grout are alternatingly introduced into the hole whilewithdrawing the vibrator arrangement 30 from the hole, wherein the groutflows into the gravel and fills spaces between gravel stones so that,finally and after curing, the concrete pile 13 is formed. The grout alsoflows into spaces of the material column surrounding the hole, so that ahigh friction between the concrete pile 13 and the material column canbe achieved.

According to yet another example (not illustrated), an auger is used todrill a hole into the material column 12 and the pile 13 is formed as aconcrete pile in the drilled hole. Forming the concrete pile maywithdraw the auger from the ground and may include the same method stepsexplained above with regard to forming the concrete pile after entirelywithdrawing the vibrator arrangement 2 from the ground 100.Alternatively, the hole is filled with concrete when withdrawing theauger from the ground 100, wherein a reinforcement cage 14 may beinserted after withdrawing the auger from the ground 100.

The pile 13 may be formed such that it essentially has the same diameteralong its length. This, however, is only an example. According toanother example, the pile 13 has a varying diameter. According to oneexample, the pile diameter increases towards the ground surface 101.

According to another example illustrated in FIGS. 5A and 5B, forming thepile 13 includes driving a pile 13 into the material column 12. Drivingthe pile 13 into the material column 12 may include using a conventionalramming or hammering device 5, which is only schematically illustratedin FIGS. 5A and 5B, or may include any other kind of device that issuitable to drive a precast pile into the ground, such as a topvibrator. In this example, the pile 13 may be comprised of any kind ofrigid materials, such as concrete, steel, timber, or combinationsthereof. According to one example, the pile 13 is a precast concretepile that includes a steel reinforcement cage.

The foundation of the type explained above with a material foot 11spaced apart from the ground surface 101, a material column 12 on top ofthe material foot, and a pile 13 in the material column may form a partof a solid foundation for any kind of structure. By virtue of the widematerial foot 11 the arrangement is capable of bearing high loads evenwhen the material foot 11 is formed in an initially relatively weakground, such as compactable sand. In particular, when forming thematerial column 12 using a vibrator arrangement, vibrator 23(horizontally vibrating depth vibrator) arrangement compacts the groundlayers by vibrations inducing horizontally polarized shear waves and bydisplacement, while other displacement tools and/or vertically vibratingtools can only compact with limited effect by displacement only.

The load bearing capability of the rigid body is, inter alia, dependenton a friction between the material column and the surrounding soil and aload bearing capability of the material foot 11. The load bearingcapability of the material foot 11 is dependent on the diameter of thematerial foot 11 and the load bearing capability of the soil region inwhich the material foot 11 rests. There may be scenarios in which a highfriction between the material column 12 and the surrounding soil isdifficult to achieve or technically not wanted, for example, because ofunstable soil layers. In this case, the material column 12 may be formedfrom a material providing a low friction, such as sand or round (river)gravel. Using this type of material may result in an easiermanufacturing of the concrete pile 13, either because the vibratorarrangement 30 can penetrate into the material column 12 more easily, orbecause a precast concrete pile can be rammed into the material column12 more easily.

When forming the pile 13 using a vibrator arrangement or when rammingthe pile 13 into the material column (and the material foot 11) mayfurther increase the lateral confinement stress in the material column12 and the material foot 11, and may further increase the diameter ofthe material column 11 and the material foot 11.

FIGS. 6A and 6B illustrate another example of a method for forming theconcrete pile 13 in the material column. Referring to FIG. 6A, themethod includes driving a hollow tube 71 that is closed at a bottom endby a shoe 72 into the material column 12. Driving the tube 71 into thematerial column may include using a vibrator (not shown). Further,referring to FIG. 6B, the method further includes filling the tube 71with liquid concrete or with gravel and grout, and removing the tubefrom the ground, thereby forming the concrete pile 13. The shoe 72remains in the material column 12 of the foot 11 after removing the tube(lost shoe). Optionally, a reinforcement cage is installed in the tube71 before filling the tube 71 or after filling and withdrawing the tube71.

In each of the examples explained above, the pile may be formed in sucha way that it extends to the ground surface 101. This, however, is onlyan example. According to another example, the pile 13 is formed in sucha way that its upper end is spaced apart from the ground surface,wherein a distance between the upper end and the ground surface 101 isbetween 0.5 and 1.5 meters, for example. A so called load transferplatform may be formed between the upper end of the pile 13 and theground surface. The load transfer platform may include compacted crushedgravel with layers of reinforcement (geogrids and the like).

In the method explained above, the material column 12 which is producedprior to forming the concrete pile 13 (and which may be installed withvariable diameter, i.e. a stronger diameter in a weak soil layer 130 ascompared to a smaller diameter in stiffer/denser soil layers 140)stabilizes the ground before forming the concrete pile 13. Thisstabilizing of the ground 100 is more intense in weak layers than instronger soil layers. Forming the material layer 12 pre-stresses thesurrounding soil laterally, wherein by such pre-stressing it can beprevented that liquid concrete of the concrete pile expands in such weaklayers under its self-weight, which would lead to the well-knownbottlenecking effect as shown in FIG. 7 (see 61). Thus, unlike in aconventional method, bottle necks in the concrete pile can be avoided.This is explained with reference to FIG. 7 in greater detail.

FIG. 7 schematically illustrates a concrete pile 6 that has been formedby drilling a hole in the ground and filling the hole with concrete. Inthis method, however, the hole needs to be drilled down to a solidregion, such as bedrock 110, so that the hole must not end in arelatively loose region such as compactable sand region 120. Further,the weight of the concrete before curing provides a load to the groundsurrounding the hole. This may result in an unwanted varying diameter ofthe concrete pile, wherein the weaker the surrounding material, thelarger the diameter. Moreover, in the region of an interface between aweaker ground region 130, such as a soft clay region, and a more rigidregion 140 above such weak region, such as a sand region a bottle neckmay be formed such that the concrete pile 61 locally has a diameter thatis smaller than the diameter of the hole formed before. In the worstcase the pile would be interrupted at such a transition zone betweenstrong soil 140 and weak soil 130 and no longer be contiguous over itsfull length.

The material column 12 explained above may be omitted. According to oneexample, forming a foundation without the material column may includeforming the foot 11 in accordance with one of the methods explainedabove and forming the pile 13 in the hole that remains above the foot 11after installing the foot 11. Forming the pile 13 may include any one ofthe pile forming methods explained above. A foundation formed in thisway is illustrated in FIG. 8.

According to one example, the pile 13 is a precast pile in accordancewith any of the examples explained above and has a diameter that islarger than a diameter of the hole remaining above the foot 11. The pile13 is driven into the ground using any kind of driving device, whereinthe hole provides a guidance for the precast pile 13.

Although various exemplary embodiments of the invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications can be made which will achieve some of theadvantages of the invention without departing from the spirit and scopeof the invention. It will be obvious to those reasonably skilled in theart that other components performing the same functions may be suitablysubstituted. It should be mentioned that features explained withreference to a specific figure may be combined with features of otherfigures, even in those cases in which this has not explicitly beenmentioned. Such modifications to the inventive concept are intended tobe covered by the appended claims.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

1. A method comprising: forming a foot in the ground; forming a material column on top of the material foot; and forming a pile in the material column such that the pile extends down to the material foot or into the material foot.
 2. The method of claim 1, wherein forming the foot includes forming the material foot using a vibrator arrangement.
 3. The method of claim 2, wherein the vibrator arrangement includes a laterally vibrating vibrator.
 4. The method of claim 1, wherein forming the foot includes introducing material into the ground.
 5. The method of claim 4, wherein the material includes at least one of a granular material; grout; or concrete.
 6. The method of claim 1, wherein forming the foot includes compacting ground material.
 7. The method of claim 2, wherein forming the material foot includes: introducing the vibrator arrangement to a predefined depth into the ground; and repeatedly lifting and lowering the vibrator arrangement, wherein material is introduced in a space below the vibrator arrangement when the vibrator arrangement is lifted and the vibrator arrangement penetrates into the introduced material when the vibrator arrangement is lowered.
 8. The method of claim 7, wherein introducing the vibrator arrangement into the ground includes predrilling a hole into which the vibrator arrangement is introduced.
 9. The method of claim 1, wherein an average diameter of the material foot, and wherein the diameter of the material foot is between 2 times and 5 times the diameter of the vibrator arrangement.
 10. The method of claim 1, wherein an average diameter of the material foot is between 0.5 meters and 2 meters.
 11. The method of claim 1, wherein forming the pile includes: introducing a vibrator arrangement into the material column (12) and forming the pile (13) using the vibrator arrangement.
 12. The method of claim 11, wherein the pile includes at least one of concrete, gravel, and grout.
 13. The method of claim 1, wherein forming the pile includes: ramming with a ramming device a precast pile into the material column.
 14. The method of claim 13, wherein the pile includes at least one of concrete, steel, and timber.
 15. The method of claim 1, wherein forming the pile includes: drilling a hole into the material column and filling the hole with concrete.
 16. The method of claim 1, wherein forming the pile includes: installing a hollow tube in the material column; filling the tube with concrete; and removing the tube.
 17. The method of claim 1, wherein forming the pile (13) comprises forming the concrete pile (13) to include a reinforcement cage (14).
 18. The method of claim 1, wherein forming the material column includes forming the material column to have a diameter that varies along a length of the material column.
 19. The method of claim 1, wherein forming the material column includes repeatedly lifting and lowering the vibrator arrangement at a plurality of different positions in the hole, wherein material is introduced in a space below the vibrator arrangement when the vibrator arrangement is lifted and the vibrator arrangement penetrates into the introduced material when the vibrator arrangement is lowered.
 20. The method of claim 19, wherein repeatedly lifting and lowering the vibrator arrangement includes: measuring an operating parameter of the vibrator arrangement when the vibrator arrangement is lowered, and repeatedly lifting and lowering the vibrator arrangement until the measured operating parameter at each of the plurality of different positions has reached a predefined threshold.
 21. The method of claim 20, wherein the at least one operating parameter is selected from the group consisting of: a power consumption of the vibrator arrangement; an acceleration of the vibrator arrangement; or a velocity of the vibrator arrangement. 